Hi, I'm Mark with Kimray, where we help energy producers solve their biggest
control challenges. Today, we're going to follow the pipes on an oil and gas well
site from the wellhead to a gas production unit.
Here at this wellhead, gas is being injected into the casing to pressurize the well, which is a process
called gas lift. There are certain connections on the side of the tubing
that let gas into the tubing which is atomizing the liquid which allows that
liquid to become lighter and rise to the surface. That fluid and gas in the well
is sent over to the gas production unit to be processed.
A gas production unit is
actually two pieces of equipment joined together inside one housing. On the left
there's a line heater, on the right there's a separator. Let's see what
information we can gain from looking at the coils inside the line heater.
The GPU has a coil made up of continuous passes of piping. The tag here tells us it's
made up of 2.5", 7700-pound working pressure coils on the
preheat side of the choke, and 3", 3200-pound coils on the
expansion side of the choke. These coils are immersed in a water/antifreeze
solution that acts as a heat transfer media. That solution is heated by a fire
tube contained in the heater section of the GPU. All of these components are
needed because the pressure of the wellbore is higher than that of the
pipeline to which the gas is being delivered. When you have a pressure drop,
you have a temperature drop as well. With that temperature drop, freezing can occur
or hydrates will form and both of those issues can cause problems for the
producer. The GPU will preheat the well stream before it comes to the choke
which is where the pressure drop and corresponding temperature drops take place.
The well stream is then heated and allowed to expand prior to entering the
separator for further processing.
We're going to follow this 3" pipe coming out of expansion loop of the coils.
Here's the inlet to this 3-phase horizontal separator which is a 1440-pound working pressure vessel,
approximately 10' long and 36" in diameter. There are two types of these
vessels: weir and interface. This one is using a weir system.
There's an inlet diverter inside and the well stream breaks up as it hits against it.
Inside this separator are two baffles.
Water goes under the first baffle, flows
through the weir nipple to establish a water level through the whole length of the separator.
The oil then flows over the top of the first baffle into the oil dump chamber.
If this were using an interface system there's only one baffle involved.
The water controller on the right establishes an interface which allows
the oil to spill over into the oil chamber. In either system, the water is
dumped through this outlet and goes downstream for disposal or storage.
Now let's follow the pipes that carry the oil.
This oil goes to a meter which is
recording the amount of liquid coming through the dump valve. That pipe
continues to an oil storage facility located off-site for processing or sales.
The horizontal separator is half full of liquid. This means the top part of the
separator will be filled with gas. The gas will go to sales and will also be
used to power various instruments controlling this unit. There's a mist
extractor inside the vessel located approximately here. The mist extractor
extends just below the liquid level that forces the flow of gas through the
extractor. Instrument gas refers to the gas needed to run the controls for the
unit. This half-inch line goes in and turns up and that's where you'll get the
highest driest gas possible which is what you want for instrument gas.
This gas continues through a preheat line because there will be another pressure
drop that could result in freezing. The instrument gas then flows into a first
cut regulator, in this instance cutting the pressure down from 200 pounds down
to 70, resulting in a 10-12 degree temperature drop before going into the volume pot.
The volume pot allows a place for
liquids to drop out of the gas as a result of that pressure and temperature drop.
If wet gas gets into controls they can deteriorate quickly.
Then we're taking a second pressure cut, this time going from 70 pounds down to 30 pounds.
The second cut is for instrument gas for the controllers.
As we continue to follow the pipe, we see the emergency shutdown device used to shut down the wellhead in
case of an emergency or process failure.
This system is the burner manifold with
two Kimray thermostats and one burner valve. One thermostat is monitoring gas
temperature the other monitors water bath temperature. If the set point of
either thermostat is reached, gas going to the burner valve is shut off.
The small tubing line coming off the burner valve supplies gas to the standing pilot
light located in the flame arrestor. This is a 150 PG pilot set in the indirect mode.
As we trace that out, we have a sensing line, supply line, and output.
This line goes all the way down to the other end of the gas unit where the sales line is located.
There's a pressure-to-close valve used as a back pressure valve to
ensure that we have the necessary pressure to push liquids to their final destinations.
After leaving the back pressure valve, the gas continues to
a meter run where it is measured and sold.
Want to learn more about oilfield equipment?
Watch the next video in our oil and gas 101 series about rod pumps,
two-phase vertical separators, and heater treaters.